This project is aimed at the study of the properties of membrane proteins that underlie important biomedical processes and/or are implicated in health disorders and how they interact with their membrane environments. By means of the latest one and two-dimensional electron-spin resonance (ESR) methodologies and nitroxide spin-labeling methods, we will directly observe significant protein functional changes, and in parallel experiments observe the changes occurring in the dynamic structure of the membrane lipids. This ability to accurately characterize both membrane host and membrane protein is an innovative approach in this project on the role of membrane-protein interactions in the protein's function. Specific projects include the following: Study of the effect of fusion peptides and transmembrane domains on membranes will be continued. Recent results showed that the influenza hemagglutinin (HA) fusion peptide (FP) cooperatively increases ordering of the membrane headgroup region. To determine if this membrane ordering effect is common for other entry of envelope viruses, the effect of HIV gp41 fusion peptide and Ebolavirus internal fusion loop will be studied, including their aggregation. In the second project on the dynamics of antigen-mediated clustering of Immunoglobulin E (IgE)-receptor (FceRI) complexes in membranes, it will be determined how protein-lipid and protein- protein interactions dictate their first steps. This study will build upon our recent successes in developing ESR methods to characterize the changes in membrane structural dynamics upon activation. In a third project, tau, a protein important in neurodegeneration will be studied. The molecular basis for tau interactions (and of its disease-linked mutations) with membranes will be addressed. These studies will benefit from our successful project on another intrinsically disordered protein, alpha synuclein. A fourth project will be directed to deter- mine the effects of bilayer properties on th functional dynamics of the glutamate transporter GltPh, an archael homologue of mammalian glutamate transporters, building on recent ESR studies in these labs. In a fifth project our recent ESR studies on the mechanism of transmembrane signaling in bacterial chemoreceptors will be continued and extended. In particular, the participation of membrane lipids will be addressed, including how the bilayer itself changes upon receptor activation, as well as the concomitant changes within the receptors. In all these studies, the modern ESR techniques of Pulse-Dipolar ESR (PDS) (which includes both double electron-electron resonance (DEER) and Double Quantum Coherence (DQC)-ESR) will be used to characterize membrane protein functional changes, and the techniques of multi-frequency ESR and Two-Dimensional Electron-Electron Double Resonances (2D-ELDOR) will be utilized to characterize the concomitant changes in dynamic structure of the membranes. These studies will involve extensive collaborations with leading research groups. Possible clinical applications include detection of membrane changes during immune response, prevention of viral entry, neurological disorders, and development of anti-microbials.